One example of a stage device of this type will be described with reference to FIGS. 1(a) and 1(b). In FIGS. 1(a) and 1(b), two guide rails 2 and 3 are disposed on a surface plate 1 so as to be parallel to each other with a predetermined distance therebetween. The guide rails 2 and 3 each extend in a Y-axis direction shown in FIG. 1(a). Moving bodies 4 and 5 are mounted on the guide rails 2 and 3, respectively. Herein, the guide rail 2 and the moving body 4 will be described. As shown in FIG. 1(b), the moving body 4 is provided with static pressure bearing pads 12. The static pressure bearing pads 12 are interposed between the guide rail 2 and the moving body 4. The moving body 4 is also provided with a static pressure bearing pad 13. The static pressure bearing pad 13 is interposed between the surface plate 1 and the moving body 4. By this, the moving body 4 is movable along the guide rail 2 in the Y-axis direction.
Likewise, the moving body 5 is also provided with static pressure bearing pads 12 and 13. The moving body 5 is movable along the guide rail 3 in the Y-axis direction.
A beam 6 is laid between the moving body 4 and the moving body 5. The beam 6 extends in an X-axis direction shown in FIG. 1(a). The beam 6 has one end rigidly fixed to the moving body 4 and the other end joined to the moving body 5 through a plate spring structure 8. The fixation between the moving body 4 and the one end of the beam 6 is carried out, for example, by the use of screws. By this, the beam 6 is movable in the Y-axis direction along with the moving bodies 4 and 5.
A moving body (movable portion) 14 is mounted on the beam 6. The moving body 14 is movable in the X-axis direction using the beam 6 as a guide. Static pressure bearing pads 14a to 14c are disposed between the surface plate 1 and the moving body 14. The static pressure bearing pads 14a to 14c are attached to the moving body 14. By this, the moving body 14 is guided by the static pressure bearing pads 14a to 14c in a Z-axis direction with respect to the surface plate 1 and movable in the X-axis direction.
In FIG. 1(a), the moving body 4 is shown with a portion thereof removed, while the moving body 14 is shown with an upper portion thereof removed.
A static pressure bearing pad 15 is attached to a lower surface of the beam 6 at its center portion. The static pressure bearing pad 15 is interposed between the surface plate 1 and the beam 6. By this, the beam 6 is supported by the static pressure bearing pad 15. That is, the static pressure bearing pad 15 moves along with the beam 6 over the entire strokes in the X-axis direction and the Y-axis direction without impeding the movement of the moving body 14 while supporting the self-weight of the beam 6 and thus supports the beam 6 so as not to apply excessive loads to the joining portion between the beam 6 and the moving body 5, and so on. Such a stage device is disclosed, for example, in Japanese Unexamined Patent Application Publication (JP-A) No. 2000-356693 (hereinafter referred to as Document 1).
As drive sources of the moving bodies 4, 5, and 14, linear motors are normally used. For example, the linear motors are formed between the guide rail 2 and the beam 6 and between the guide rail 3 and the beam 6, respectively, so that the moving bodies 4 and 5 serve as movable portions. Further, the linear motor is formed between the beam 6 and the moving body 14 so that the moving body 14 serves as a movable portion.
In the case of using a moving coil type linear motor, description about the linear motor, for example, formed between the guide rail 2 and the beam 6 will be as follows. A plurality of permanent magnets are arranged at regular intervals along the guide rail 2. A plurality of permanent magnets are arranged with a gap defined with respect to those plurality of permanent magnets so that different magnetic poles face each other. Then, a movable coil joined to the moving body 4 is disposed in the gap so as to be movable along with the moving body 4.
In such a stage device, in addition to the foregoing structure, each linear motor is provided with a position sensor in the combination of a linear scale and a linear sensor for position control of the moving body 4, 5, or 14. Further, synchronous control is implemented with respect to the linear motors for the moving bodies 4 and 5. Such a stage device is disclosed, for example, in Japanese Unexamined Patent Application Publication (JP-A) No. 2000-155186 (hereinafter referred to as Document 2).
In such a stage device, a table for placing thereon a member to be processed or the like is installed on the moving body 14 and drive control is implemented for accurately positioning the member to be processed.
On the other hand, in such a stage device, it is necessary that the beam 6 be orthogonal to the guide rails 2 and 3 for accurately positioning the member to be processed. This is because positioning specification of the member to be processed is carried out by the use of X-coordinate and Y-coordinate on the surface plate 1. The stage device so far uses, as a criterion, an orthogonality based on machine accuracy at the time when the beam 6 is located at a certain reference position (reference coordinates), for example, at an origin position set close to an end portion of one of the guide rails 2 and 3. Thereafter, when the moving bodies 4 and 5 are subjected to position offset, the moving bodies 4 and 5 are individually controlled in position so as to maintain the foregoing orthogonality based on the machine accuracy within a predetermined range.
However, in the stage device of this type, when continuous operation is carried out, the respective members, particularly the beam 6 and its peripheral members, may be subjected to deformation due to heat generation of the linear motors. As a result, the orthogonality of the beam 6 with respect to the guide rails 2 and 3 may deviate from the foregoing predetermined range. That is, in the stage device so far, when the continuous operation is carried out, the respective members in the stage device are subjected to temperature rise due to the heat generation. There has been a problem that when the orthogonality of the beam 6 changes thereby, the orthogonality of the beam 6 with respect to the guide rails 2 and 3 cannot be maintained within the predetermined range and thus the accurate positioning cannot be achieved.